1. Field of the Invention
The present invention relates to a method of removing hydrogen sulfide from sour liquefied petroleum gas.
2. Description of the Prior Art
Liquefied petroleum gas mainly consists of a mixture of propane, normal-butane and iso-butane. As used herein, the term "butane" refers to normal-butane, iso-butane and mixtures of normal-butane and iso-butane. Sour liquefied petroleum gas is liquefied petroleum gas which contains hydrogen sulfide. Sweet liquefied petroleum gas is liquefied petroleum gas which is relatively free of hydrogen sulfide.
Gaseous streams containing butane and lighter hydrocarbons are obtained in a refinery as gaseous overhead, for example, from a crude distillation column, or from fractionating a hydrocarbon-containing stream obtained by converting a heavy hydrocarbon-containing feed. Such a conversion method can be catalytic cracking or hydrotreating.
There are several methods to obtain a liquefied stream from the gaseous overhead. The gaseous stream can be compressed to a pressure from 10 bar to 30 bar (gauge) or it can be mixed with gasoline. Still additional methods involve chilling the gaseous stream or absorbing it in lean oil.
Liquefied petroleum gas is also obtained as by-product from the production of natural gas or hydrocarbon oil from an underground formation.
The present invention is directed to the removal of hydrogen sulfide from sour liquefied petroleum gas. Hydrogen sulfide is normally removed from sour liquefied petroleum gas by contacting the sour liquefied petroleum gas in an extraction column with a liquid and regenerable absorbent. Suitable absorbents include aqueous solutions of di-isopropanol amine or diethanol amine. An example of such a process is described in European Patent Application Publication No. 21 479.
The liquefied petroleum gas obtained after the removal of hydrogen sulfide contains contaminants such as absorbent, water and iron compounds. Although the liquefied petroleum gas containing contaminants can be used at the refinery, the contaminants need to be removed.
The present invention provides a method of removing hydrogen sulfide from sour liquefied petroleum gas which yields a stream of sweet liquefied petroleum gas that is substantially free of contaminants.